Hey guys --
Thanks for all the replies. Also I've been trying to find the technical te= rm for this hole in the concrete and seems most call it a dap out or block = out. FYI on that :)
As for solutions, I've thought about using a foam spray, but I've heard ant= s and other varmints can actually be attracted to it and over time it would= n't hold up. I also heard some people using roofing tar, but again I'm not= sure if that would last as concrete would. I just wasn't sure if there we= re any reasons for not doing concrete from a construction standpoint, but f= rom reading other articles it seems it's common to fill this in for the ver= y reason I'm wanting to do it. Unfortunately for us our tub is right next = to an outside wall so the trap is literally less than a foot from the outsi= de... and with the ground sloping up to the house at almost a 45 degree ang= le this means ants or any other critters only need to go horizontal in the = ground for about 18 inches to two feet and they're under the trap. =20
So unless there's some really huge reason not to fill it in I'll probably m= ake this a project for an upcoming weekend to put a generous layer of boric= acid down then cover the hole in concrete. SHould I put some pee gravel d= own or something down first though or just put concrete right over the sand= ? =20
We have another tub in the second bathroom, but it's more centrally located= in the house about 20 feet from an exterior wall. I don't have as easy acc= ess to that area as I do in the master (garden tub with removable side) so = hopefully that tub isn't another source for ants coming in -- but we'll see= over time if it continues to be a problem. If I have to rip out drywall to= get to it I can in a closet. But the Master bath seems to be the biggest = source of unwanted things entering the house.
Thanks for the advise...