On Thursday, December 19, 2013 8:36:59 AM UTC-5, Unquestionably Confused wrote:
On 12/19/2013 7:20 AM, TimR wrote:

On Wednesday, December 18, 2013 11:40:27 PM UTC-5, Irreverent Maximus

wrote:



Idle speculation: if the vacuum got the water started over the

top of the P-trap, a siphon would be created that would not stop

until all the water had been removed.



[snip]



Oh, all right, I will. When I was in college I once saw a gadget the

kids called a bong, I dunno if it has an engineering name. I'm not

sure the usage is entirely legal.



It had a trap filled with smelly water, but differential pressure was

sufficient to pull heated air through water and out the top.



However it did not have an operable vent stack between the trap and the

orifice to which you applied the necessary vacuum. If you recall

otherwise it must have been some really good heated airg

Sigh, and completely different settup. It's kind of the reverse of a
P-trap. It's designed to let AIR pass through water. If it was
designed like a P-trap with a blocked vent, you'd be sucking the
water out until you finally got to the air.