I have to install a check value on my sewer line. The correct way to install it is before the trap. But I may have no other choice but to install it after the trap. Can I do that?

Yes you can install the check valve after the trap. Where you live that you need both a trap and a check valve? Just curious, Tom

Yes you can install the check valve after the trap. Where you live that you need both a trap and a check valve? Just curious, Tom I live in New York City. I had got some quotes on the installation and some of the plumbers said I have to move the trap. Therefore raising the price of the job. Some people say that if there is a blockage the caps on the trap will pop off. Easy fix put a 50 pound sand bag over the caps so they don't pop off. I`m pretty handy so I`m trying to save some money by doing it self. Any other tips. Thank You

Through our the"some people"that are giving you this advice? Back to you, Tom