I have a older house and I cannot get the bath tub to completely uncloged. I think the P trap needs to be changed. The only problem is it is a cast iron screw togeather p trap and the tub sits on a slab so there isn’t any way to get under the tub. I think it is going to be a very difficult job to replace the cast iron P trap with a ABS one, because of the lack of room to work with. I was wondering if you know of a easyer way to replace the P trap