Neither coffee grinder nor waterpic would need a true sine wave inverter, and I'd think you could find a MSW 400 watt inverter for maybe $35 or so. I have such a device I got for about that amount, and it does fine plugged into the 12 volt cigarette lighter outlet in the TT. I've powered a waterpic myself from it just fine. Such a set up does not drain the house battery enough to worry about, as it's only going to be on for a couple minutes. Where you'd get in trouble would be trying to run your AC or MAKE a pot of coffee off that battery. (Obviously with a much larger inverter.)