I am thinking ahead to when I try to close my pool by myself for the first time in a few weeks. The picture below shows the three pipes coming from my two skimmers and the main drain. I need to air lock the main drain but can blow all the water out of the skimmer lines. The far left valve is for the main drain but the shut off lets water through when it's closed. The other two for the skimmers work as intended...of course . Since the main drain valve is the one I need the air lock on, can I swap the innards of one of the other shut off valves with the not quite functioning one in the main drain instead of cutting pipe?