Cleaning out crud in water jackets

[wrndln]

I have an engine with all the machine work done on it, but the place that boiled out the block didn't do a good job to say the least - a lot of crud left in the water jackets. I used screwdrivers and a broken speedometer cable in an electric drill to remove a lot of the crud. I am sure there is still some rust and mineral buildup left in the engine. I am going to use Evaporust or CLR to put in the engine, but I need to block off the inlet water port. BTW, the head is not on the block. I am trying to figure out a way to seal off the inlet port, but allow a drain to let the liquid solution out after soaking a few days. I can strain the liquid and pour it back into the engine for more soaking if necessary. It seems to me that if I use a regular inlet fitting, I could somehow make a plug to seal off the inlet, but then remove it to let the solution out after soaking. I don't want to make a big mess if at all possible. Has anyone don't this before? Any suggestions on how to make a simple one time plug with a drain would be appreciated.
Rusty Nelson