06:34AM | 04/08/08
Member Since: 11/01/06
34 lifetime posts
Hi all!

I have a (simple?) theorical question... What is the very minimal slope in order to empty a tub?

I know that (in theory) it could be just 1 degree (if you're patient!)... but in a real world case can it be say 1/8 per foot? 1/16 per foot?

Would the size of the pipe be any concern? a 1 1/4 drain is by code but what if one uses a 2" or even a 3" pipe? Would air displacement be too great that it would cause siphoning all the p-traps around a house?

Just curious!

Thanks all!


01:48PM | 04/08/08
Member Since: 01/24/06
1626 lifetime posts
Me office1
I don't know what code your using but everyone I ever used had an 11/2" tub waste not 11/4

Drainage is by fixture units = 7.48 gallon =1 cubic foot Or 1 (one) GPM from a pump discharge

When your talking tub such as a bath you set it level and even if you did want to pitch the tub and gave it a full 1" per ft or 3" feet per foot the 11/2 drain could only carry so much water. (volume)

You can go as little as 1/16 per foot pitch BUT the pipe diameter has to be a minimum of 8" and your only going to

be allowed 1140 FU as opposed to 2300 if you used 1/2" pitch


04:37PM | 04/08/08
Member Since: 11/01/06
34 lifetime posts
I made a typo... I meant 1 1/2 not 1/4! Sorry about that!

FU? No worries I know it's not the other FU! but what does 1140 FU stands for?

I've been giving this more thoughts...

At the exit of the bathtub even if I put a pipe at 0 degree the bathtub will still empties itself because the pipe is lower the drain and gravity will do its work... no matter the size of the pipe used.

Now say I put a 1 1/2 drain pipe and give it 45 degrees slope... what will be the consequence on the p-traps attached to that same waste line? I can picture the pipe filling and trying to breath but no major bad things happening... same if the pitch were 1/8 per ft. The pipe will fill itself with water, air will be pushed out and the vent will give it some more... but to a point where the volume inside the vent pipe will reach its max point and not be able to supply more air... then like a bottle you are trying to empty will caugh... am i right in this assumption?

Many thanks for your patience!


03:32PM | 04/09/08
Member Since: 07/22/04
661 lifetime posts
now you weren't paying attention.


01:47PM | 04/10/08
Member Since: 01/24/06
1626 lifetime posts
Me office1
They never do Larry, they want a crash course and then when you go into minor details they get confused with facts..Go figure.


01:10PM | 04/11/08
Member Since: 11/01/06
34 lifetime posts
I wasn't confused! I was asking about FU... now I know what it is... Fixture Unit... it would had been nice ot say that it means to a non initiated person...

we all have our own lingo...



11:22AM | 04/24/16
do plumbers always condascend to others because they know that their line of work is elementary?


11:25AM | 04/24/16
and it's not really a career but just a "chore" that anyone can learn how to do masterfully in THREE days


11:28AM | 04/24/16
if they want to stick their hands in shit for a living that is...


11:33AM | 04/24/16
don't confuse yourself with an actual civil engineer or physics major asshole just because you have learned how water flows from pipes of differing diameters....
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