One of many spring projects is i want to backflush the block to remove any built up crud.
I had water flow out of all the water lines, good amount, but I plan on putting in strainers--yea finally-- this year and want to 'spring' clean the blocks.
Is this possible without doing any harm?
I was thinking of making and adapter that fit the blue plugs and back flush that way???

I wouldn't back flush the blocks. Anything that is stuck in there is gonna still be stuck. Just run the engines on the hose with the blue plugs out to flush them.

Thanks Griff, I was wondering if it would really help at all.
I know a few years back I had one passage plug and had to use wire to free it up.
I just fear there is 'stuff' in the sides