Perhaps I'm just having massive brain fart, but I'm trying to take the petcock off so I can coat the tank with POR-15 (tank sealant).  It looks to be a 10mm bolt, but I can't ratchet it because it's bound so close together.  Looks like there's some square indentations in the center, maybe, but they're black as tar so I'm honestly not quite sure.  Are there square tools, I have a hex and oct, but square? So, what tool / technique do I need here?

Two asides:  Anyone know a good way to completely drain the tank?  (Will removing the petcock do it?)  I can still hear water sloshing around in it and can't seem to make it all come up the keyed eneterance whole

Do I need to remove the electronics to coat the interior of the tank?  I figure it doesn't matter because all the nasty stuff's going inside and there's likely to be no contact.

Ah!  I see, there's a philip's head hold there, it's just been stripped so it looks almost square.  Bleh, oh well, got a few days to find a replacement.