Meh... Instead of toilets, I always wondered why they didn't just step onto a transporter pad, not actually go anywhere, and just step off a few ounces/pounds lighter.
E=MC^2 stream redirected to engines, replicators, or weapons as needed.
Hell, just taking a surplus redshirt, and beaming him over to, or even just near the offending Romulan Warbird, or Borg Cube, and not letting him rematerialize properly would be pretty darn effective. Done in low orbit over a planet, it's probably enough to make the facing half of the planet slightly molten, and blow off the atmosphere.
Edit, because I was stupid and pressed Post before typing a response...
Beaming a redshirt
, or a large hunk of rock, into low orbit would not be quite that impressive. A photon torpedo, with a yield of about 67 megatons, utilizes 1.5kg of antimatter (presumably reacting with the torpedo casing and other materials for 3kg of M-AM). A 75kg redshirt (or rock) would produce, at most, 25x more boom, and probably considerably less than that IMO.
A quantum torpedo, such as those fired by the Enterprise-E against the Borg Cube in
First Contact, was supposed to utilize zero-point energy to produce a "dialable" yield up to 200 megatons. You want true planet-killing capability, you use something like a Genesis device, or use the ship's probes and/or torpedoes to destabilize the local star.
And FTR, Enterprise-D (Picard's ship from the Next Generation series, the one crashed by Troi in
Generations) only had ONE bathroom on the whole ship - right by the Captain's Ready Room, IIRC.
