How best to clean old 78s.

This might be quite an adventure! First of all you cannot be sure of what you have. And you would not want to play them on a high end system unless you have a 78 cartridge such as Shure is making. So, begin with examination. Are they gritty grimey? Then start with a nice wash under the tap. No rubbing! Are they just dirty, then use purified water liberally. You can use clean dish towels as a work surface and the great brushes that Disk Doctor makes. You are going to need his cleaning consentrate anyway (no alcohol!)so you may as well just order his whole kit with a pint or quart of fluid. Are they mildewed? Then you need an enzyme cleaner. Try Bugtussel. After you do the prelim wash(es), you are ready to use the good Doctor's fluid and brush for the clean. Change base towels as needed. He encloses comprehensive directions so I will not repeat. Just know that nothing else is as good, safe or easy as DD. Do the final purified water rinse and dry. Then use Last record preservative. You will see the surface drink it in. It seals without sonic residue. It reduces friction to put less wear on the stylus and less noise in the play. A clean new sleave, preferably acid free paper, and you are done. Best wishes. It ain't digital, but it has a sound of its own which has an artful immediacy.