Just a couple months ago, I finally got around to putting a fill loop in on mine. Just tee'd into the water line on the discharge side of the water pump and put a ball valve in a loop connecting back on the suction side.
On the suction side I teed back in at the place where thor had put the antifreeze suction port...and added a second valve along with a length of tubing for making that antifreeze job a bit easier.
It was an easy job. 'Hardest' part was modifying the cabinet panels that access the pump area so that I could pull them off without tools....and that was no more trouble than installing some spring catches.
I would have loved to get a panel mount valve and mount on a bulkhead like rcharrette's picture, but that would have been a whole other set of issues...
Instead I just went with a cheap basic ball valve.
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