The sludge trap plugs are difficult to remove at best. I use drag link sockets on the end of an impact wrench (the kind you hit with a hammer, not an air impact) and clamp the flywheel of the crank in a large vise. A drag link socket is like a socket that has a big screw driver blade that was used to dismantle tie rod ends in Model A Fords and some Chevrolets into the early 1950's. I also grind the end of the drag link socket so it's curved to fit tightly in the sludge trap plug. On top of this I then heat the crank up with a torch. On cranks where the sludge trap plugs have never been removed the threads are center punched so the plug can't back out. IF the plug has been removed people have often drilled the center punch and then center punched it again once the plug is screwed back in. The first few times I removed plugs I would drill the center punch. Then I decided it was better to force it out even if it ruined the threads on the plug and then just clean up the threads in the crank with the correct large tap and install a new plug with loctite. On the one A10 motor I put together and ran long enough to actually wear it out ( 15 years of near daily transport) I found very little crud in the sludge trap when I opened it up again.
With this in mind it's a real ordeal to get the sludge trap plugs out when the crank is out of the engine. Trying to get the sludge trap plug out through an access hole in the side of the engine would really be difficult. Besides, with modern detergent oils and half way regular oil changes cleaning the sludge trap out at each engine rebuild is plenty often. When I've found really dirty sludge traps its when the engine was last used during the non-detergent oil era ( 50 years ago) and has never been rebuilt. With modern detergent oil the sludge trap just won't fill up with crud like they used to with the old non-detergent oil. If you are really concerned about clean oil just change it more often and if you are really worried install an oil filter in the return line.
