I live in a 1963 houes with 4 stacks and each with a clean out. The prior owner obviously never used the clean outs because they have 3 layers of paint on them. I am unable to open any of the clean outs and I have two drains that will not empty on the first floor. Any trick besides brunt force to open these. They ate cast iron pipe with a brass bolt plate. There is dried plumbers cement in the grooves.

Any help would be appreciated.

Forget the clean outs, go through the toilets.

The cleanout covers are made of brass. When I rfun into a stubborn cleanout cover I take a hammer and chisel and try to break it free. Failing that I take my hammer and break out the cover ithe center and pull it outinpieces. Cleanout covers are replacable in brass, PVC and ABS at any plumbing store. If you don't wish to pull a toilet or break out a cleanout cover you can always send a snake down a roof vent. Good luck, Tom

I can't use the toilet. I need to open the clean out so I can divert my sump pump to the clean out for two to three hours. My sump line drain is a gravity feed to the sewer that appears to have broken or clogged. The pump goes off every three to five minutes and the basin fills in ten since the water is just recycling into the basin when it is pumped out.
In order to snake the line, I need to divert the sump. Only sewer line access with 50 ft is the clean out

Get some paint remover they also have remover for stubborn thread sealant and get as much off as posible, then take your pipe wrench add a pipe for leverage and break that bad boy loose. If its brass just hit hard with a chisel in the middle by the nut part and break that bad boy out, You must remove the clean out so you can keep you drains clear by snaking every year needed or not.