There are several good initial spawn points but the one I prefer and that seems to be most consistent is the one spawn point in the basement of the kitchen. I use Gamecube so I'm not sure if this strat will be as consistent on PS2 or Xbox.

From here, run into the next room of the basement and grab the rocket launcher. Run back to the base of the stairs and fire a single shot into the the ceiling at the top of the stairs. This should kill two of the squid that run through the door at the top of the stairs. Stay where you are, in a few seconds two or three more squid should run through the same door. Sometimes a few more come through the door a few seconds later. If so, then you can rack up about 7 kills in 12 seconds. But what you want to avoid is any squid that come through that door with a rocket launcher or homing launcher. If they come through the door with those weapons, they tend to blow themselves up. With practice, you'll get a feel for when to run up the stairs, either after the second or third group. Hopefully when you do, there won't be a squid blocking your path.

After you run up the stairs and out the door, quickly look to the left to see if there are any squid that you can shoot. There's usually one or two here. Then run all the way around the table on the right until you're at the end of it near the square column and facing the door that leads to the toilet as well as the door that leads outside. From here you can monitor all four entrances into the kitchen. Be ready for when squid enter the kitchen. Some will have flamethrowers and some will have either of the two launchers. Just pick them off before they can shoot or flame you. It's best to use the rocket launcher here. Just shoot rockets at the ground near their feet or at walls near them. Eventually you'll run out of rockets so you'll have to pick up more in the kitchen that were dropped by squid. Pick up more ammo quickly and run back to where you were and just stay here until you have 20 kills.

Eventually you'll get that dream run where the squid constantly stream into the kitchen. Good luck on the sub-40.0!