# Another grease trap vent question



## stillaround (Mar 11, 2009)

The plans I have for a Dairy Queen show a 3" vent drawn for an exterior 1050 gal grease trap.......I get the interior grease trap vent and flow control stuff but for an exterior I have no need I can think of that requires an exterior grease trap having a vent come back into the building thru the roof.,....never seen it before.....and this is Florida for crying out loud.....

I called the inspector and he didnt want to get involved...said if its on the plans why not give them what they want....well the mechanical and plumbing part isnt a stamped plan...only the architecturals.....this job sup...is a Georgia boy and a tad stubborn ....the rest of the plans had individual vents at every fixture...well we wet vent in sunny Florida and I wouldnt give them the stupid vents there....I find confrontation all too easy when someone is trying to make me do something unnecessary, not code and on my nickel........is there supposed to be one?


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## plumbdrum (Nov 30, 2013)

It's a chamber vent, and it is required. 4" required here in Ma.


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## justme (Jul 4, 2012)

Our grease traps come with a 4" vent outlet on the trap and then most inspectors make us install one on the outgoing side of the trap here.


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## plumbdrum (Nov 30, 2013)

justme said:


> Our grease traps come with a 4" vent outlet on the trap and then most inspectors make us install one on the outgoing side of the trap here.



Never seen the additional vent on the outlet of grease interceptor, oil&gas separator yes. I don't think it would hurt to have an additional but I don't require on the outlet


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## plumbdrum (Nov 30, 2013)

stillaround said:


> The plans I have for a Dairy Queen show a 3" vent drawn for an exterior 1050 gal grease trap.......I get the interior grease trap vent and flow control stuff but for an exterior I have no need I can think of that requires an exterior grease trap having a vent come back into the building thru the roof.,....never seen it before.....and this is Florida for crying out loud.....
> 
> 
> 
> I called the inspector and he didnt want to get involved...said if its on the plans why not give them what they want....well the mechanical and plumbing part isnt a stamped plan...only the architecturals.....this job sup...is a Georgia boy and a tad stubborn ....the rest of the plans had individual vents at every fixture...well we wet vent in sunny Florida and I wouldnt give them the stupid vents there....I find confrontation all too easy when someone is trying to make me do something unnecessary, not code and on my nickel........is there supposed to be one?



And to answer your question of why it's needed ( although you should know this ) the vent is equalizing the pressure in the tank as the water flows in.


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## stillaround (Mar 11, 2009)

plumbdrum said:


> And to answer your question of why it's needed ( although you should know this ) the vent is equalizing the pressure in the tank as the water flows in.


Never seen one yet....I do understand how it could help....maybe I should differentiate and say grease interceptor...

1003.5.2 Construction of Interceptor. Each interceptor
shall be prefabricated or field fabricated and have at the
minimum one baffle that shall extend the full width of the
interceptor, extending from the bottom to within six (6)
inches of the top. The baffle shall have an inverted long
radius elbow fitting or other approved means equivalent in
size to the inlet piping but in no case less than four (4)
inches in size installed in the inlet compartment side of the
baffle with the fitting placed twelve (12) inches above the
bottom of the interceptor. Minimum depth of the liquid
shall be forty-two (42) inches. Each compartment shall be
accessible with a minimum clearance of eighteen (18)
inches square or in diameter.
1003.5.3 Inlet and outlet piping. The inlet and outlet piping
shall have a two-way cleanout tee installed. Inlet piping
shall enter at two-and-one-half (21
/2) inches above the
invert of the outlet piping. Inlet piping shall extend to
twenty-four (24) inches below the water level.
The outlet pipe shall start at eight (8) inches above the bottom
of the interceptor and extend vertically to a tee. The
tee and pipe shall be no less than four (4) inches in diameter.
The tee shall be installed with the run in the vertical orientation.

Si I have vented building drains, a free flow of air on the city sewer side and construction that allows air......oops see below


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## stillaround (Mar 11, 2009)

1003.12 Venting of interceptors and separators.
Interceptors and separators shall be designed so as not to
become air bound where tight covers are utilized. Each interceptor
or separator shall be vented *where subject to a loss of*
*trap seal.* hmmmmm..:whistling2: prolly wont make a further big deal over this.....



how would I lose a seal on a 1000 gal concrete tank?


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## plumbdrum (Nov 30, 2013)

It could get airbound


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## plumbdrum (Nov 30, 2013)

And it's not a trap, it's an interceptor, no trap seal to be lost


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## stillaround (Mar 11, 2009)

***


*** = duh


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## plumbdrum (Nov 30, 2013)

Well as an inspector I would not approve the install without the vent, also your plans call for it, your code is stating it so yes


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## GAN (Jul 10, 2012)

Yep grease trap venting is required in Illinois also

*Section 890.510 Grease Interceptor Requirements* 

Plumbing systems for institutions or commercial establishments in which grease, fats, culinary oils or similar waste products from kitchens or food processing areas are wasted, or in which grease, fats or culinary oils are wasted in connection with utensil, vat, dish or floor cleaning processes shall include grease interceptors. All waste lines and drains carrying grease, fats or culinary oil in these establishments shall be directed to one or more interceptors. (See Appendix E.Illustrations A and B.) 

a) All required grease interceptors shall comply with the following: 

1) Material and Covers. Grease interceptors shall be constructed of durable, corrosion-resistant materials and shall have water-tight covers securely fastened in place. 

2) Minimum Size. A grease interceptor installed on the same floor as the fixture shall have one-half the liquid-holding capacity of the fixture. A grease interceptor located on a floor below the fixture shall have 60 percent of the liquid-holding capacity of the fixture. To determine the liquid-holding capacity in gallons of a plumbing fixture, the length is multiplied by the width by the height in inches and divided by 231. Where two or more sinks or receptacles are connected to an interceptor the liquid holding capacity shall be based on the combined volume of the fixtures served. 

3) No grease interceptor shall receive the discharge from a food waste disposal. 

4) The flow rate of the interceptor shall be sufficient to handle the maximum demand of the connected system. 

5) All interceptors shall be installed in an accessible location to permit the convenient removal of the lid and internal contents. 

6) All interceptors shall be designed and installed with proper venting so that they do not become air bound. (See Appendix E.Illustration C.) 



Granted this is geared more for an interceptor on the interior of a structure. Illinois has been discussing dropping this requirement for the larger exterior interceptors.


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## leakfree (Apr 3, 2011)

Every building in Chicago that we've been involved with that has had a concrete exterior grease interceptor does not have any type of a vent,inside the building above or below the floor has had one...haven't had the opportunity do do an exterior one in the suburbs


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## Ghostmaker (Jan 12, 2013)

The real question that one needs to ask is do you really want to tie up the job to bring your complaint in front of the board of building standards or just put it in as designed by the architect/engineer.


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## paultheplumber1 (May 1, 2014)

I've never seen an exterior vent on an exterior one. Here it's treated as cesspool/septic system.


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## h2omanipulator (Feb 14, 2015)

I agree with your thought that it's not needed, especially if the manhole covers are not air tight - but if you must vent it, why couldn't you get away with an above grade return bend and a rodent screen? I've seen them engineered that way in my area, as opposed to going back into the structure then VTR [that seems nuts]

Our code often refers back to the MFG's installation instructions in these matters as well, maybe they'd provide you some leverage


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## Dave C. (Jul 7, 2016)

h2omanipulator said:


> I agree with your thought that it's not needed, especially if the manhole covers are not air tight - but if you must vent it, why couldn't you get away with an above grade return bend and a rodent screen? I've seen them engineered that way in my area, as opposed to going back into the structure then VTR [that seems nuts]
> 
> Our code often refers back to the MFG's installation instructions in these matters as well, maybe they'd provide you some leverage


 
you ever smell a grease trap that why it is vented up high VTR


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## Dave C. (Jul 7, 2016)

here we vent the inlet,the vessel,and the outlet .tie all 3 together above flood rim and VTR...the lids will eventually become pretty airtight and venting allows for the water to rise inside the vessel with out restriction, put a house trap on the outlet side to prevent sewer main gases from going thru your vent piping


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