joining PVC and ABS

I am in Baja Calif, Sur, Mexico. I need to join 4 inch Sanitary PVC ( very thin) to 3 inch ABS using a 4 inch/3 inch reducer. The reducer's 3 inch portion does not quite fit an ABS coupling, but it's close. Should I use ABS cement or PVC cement? I plan on filling the void between the ABS coupling and the PVC with latex/silicone calk. The only cement I have access to is either PVC or ABS cement ( I have both). Thanks.

picture of fittings

I have attached photos of the two fittings if that will help.

You're on the wrong track. You can not glue ABS and PVC together. Reason is, they have different chemical makeups. The terms "glue" and "cement" are misleading because they are neither. They are special solvents that soften the outer surface of the pipe and the inner surface of the fitting. When you join the pieces, these softened surfaces flow together and actual chemically weld the pieces together. Likewise, you can not use silicone, "glue", or anything else to fill a void in these pieces. But, there is hope. Use either ABS or PVC pipe and fittings to make the turns you need to meet the other pipe. Then use a Fernco coupler to join the two ends. Fernco coupler come in many configurations, get one of the correct size to join ABS and PVC. This is a neophrene sleeve that slips over each pipe and is then clamped with stainless steel clamps.

Thanks for the reply. Unfortunately Fernco fittings are not available in this area. Neither is ABS/PVC transition cement. I don't have anyone coming down from the States in the time frame for this project that could bring the Fernco 4 inch to 3 inch reducer or the transition cement. I will experiment and see what I can come up with.

connection

Your first mistake will be to fill the void with a sealer. You have to either use an SD to schedule 40 bushing, or cut a bell off of something and glue it to the thin pipe. But first make sure that its o.d. is the right size to slide into the ABS bell.

I hope I don't have to go to Home Depot and punch the plumbing expert in the face! I just joined some white PVC to my houses original black ABS. One pipe was the toilet drain, I cut the drain pipe and installed a new flange (White PVC). The other was my 1 1/2 bathtub drain. I was told not to use the standard purple primer when connecting ABS to PVC, I was assured by the "Homer" that it would work just fine if I simply used Oatey All Purpose cement, for PVC ABS and CPVC. These are low pressure drains will they survive????

pvc

It will probably survive, but you are supposed to use the primer on PVC regardless of the cement. You would not use it on the ABS side, however.

For bennybaby: your joint will be fine. Whether it meets code is a local issue. Some do not allow the all purpose glue and require a mechanical connection.

For pocopero: your problem is that you are mixing DWV fittings with landscape drainage fittings. They are different pipe species and are not compatible. There is an inter-species adapter, but I understand you have limited access to supplies. In your situation, a good butyl caulk might suffice.

The 1 photo of the white PVC and your statement that it is "thin" appears to me be to be a fitting that would be used outside the home. If the fittings are lose at all, as in a space between the fittings that alowes you movement without touching the other fitting even if it is only as thick as paper, the glue/cement/solvent will not work. I would suggest using an exterior rated commercial grade of caulk applied to both surfaces and then pushed together and allowed to cure/dry. JIMBO is correct. If you use the silicone caulk I would get a 100% non latex based one. I do not like latex based silicones.

Benny

all the employees at home tepo have master papers in all the trades !

actually many have 6 g pipe weld papers.

if they can't answer my questions i usually hit jiffy lube.