First replace the "Flood Safe"
They don't work with Toto, and then report back.
For more information on Flood Safe supply lines
Just installed a new Toto toilet. The shutoff valve leaks immediately as I open the valve. It would occasionally leak a drop here or there before - especially if bumped. Now it just streams out when the valve is fully open.
I had to replace the water line because the previous line was too short. I used a Flood-Safe "auto-shutoff water connector" from HD rather than the gray flexible plastic line that was there previously. could this have anything to do with it? Or do I need to replace the shutoff valve?
They are not desirable for ANY fixture. Either tighten the valve's packing nut or replace the valve.
This would be a good time to replace the old valve with a new 1/4 turn one. Toilet valves should either be fully off or fully on, no in between. The newer valves make off and on quick, easy, and positive. True, tightening the packing nut would stop the leak around the stem, but the new valves are inexpensive and while you have the water off and replacing that Flood Safe, it would be a good time to update the valve.
Well, took off the Flood Safe and used a typical flexible plastic hose. Valve still leaks. Now I have to shut off all the house water and drain the lines to replace this valve. I'm hoping it's not soldered on because then I'm removing the new toilet and likely cutting into the wall. Has any home improvement project gone as planned?
It it's just the bonnet nut that is leaking around the stem, open the valve all the way, then back it in part of a turn, take a wrench or plies and snug the bonnet nut till it quits dripping.
If that doesn't work, you may need to replace the wall shutoff.
I don't open multi-turn shutoffs all the way for just that reason. I open all the way, and then back in, I like to see the oblong handles with the long vertical showing up and down. I like how that looks.