In a previous thread down below I had this problem.

"I have an existing central AC unit and the condensate line exiting the inside air handler is 3/4" SCH 40 PVC pipe. From there is goes below grade into the concrete slab.

25' away it where it exits the house it is a 1-1/4" PVC pipe. I don't know why there is a size change, but I supposed it is OK.

Normally I would pipe in a p-trap there to stop ants, spiders, roaches from going up the condensate line. But in this case the line is 1-1/4" in size, and the bottom of this 1-1/4" pipe is only 1" above a concrete pad. There is no room to put in a 1-1/4" p-trap."

Paul suggested a reducing elbow 1-1/4X3/4 then switch to a 3/4" trap. I can't find such PVC elbow locally and I am not sure it will fit anyway since I am less than 3" from the CENTER of the 1-1/4" pipe to the top of concrete.



So for now I created a DIY trap.

I end up using a 90 elbow, followed by two 45s. I assembled them first, then turned the 90 until it touches the slab. The first 45 (labeled "A" in the picture) becomes the trap, then I "rolled up" the second 45 until the water surface in it appears to be slightly higher than the inside top of the elbow A, in other words, elbow A will be completely submerged.



That's kind of my "V" trap for now. I didn't glue anything because I need to take this thing apart every month to rinse out the algae build up.

Look OK?



Edited 1 times.

For a 1 1/2 in horizontal vent pipe I just used a fibrous filter/packing material similar to Scotch Brite stuffed in the end. Although it is in a vent pipe I am sure it would allow water to pass thru.

may be, but what would be the condition under which water would seep out? Would it back up 5' into the pipe in order for water to come out at the rate the condensate is being generated? I wouldn't want algae built up further into the pipe. Also, I don't know if rats or mice or lizards may chew through the material or pull it out.

I don't think I have a problem but I see that as your drain is at ground level your concern with mice etc.  No mater what else you may do you may want to have some sort of wire cover/insert on the end. Mice can swim.

quote; Mice can swim.

Well, I hope when they reach the 3/4" pipe, they can swim backwards.

That's backstroke.