There's video out there of some guy who cums what looks like quarts. But I understand that's done by filling up one's . . . something or other . . . via the urethra. So it might be fun to cum a quart, but I don't think I'd want to risk the damage.
The best way I've found to cum a boat-load (relatively speaking, of course) is not so much to go a long time between orgasms. It's to keep yourself stimulated for a long time. Edge. Get hard repeatedly during the day. Then take a good long time getting off when you finally decide to go for it.