The parts you'll need
A bilge pump
They are rated in gallons per hour or GPH. I used an800 GPH SeaSense brand pump which has a 3/4" outlet.
You could get an 1100 GPH pump which would pump water out faster. The 1100 GPH pump uses 1-1/8" hose which is rather uncommon. Links are on the right.
I don't really believe the GPH they claim, but mine has held up and pumps water out steadily. It does the job for me.
Here is some GE 18 gauge speaker wire. You can cut the wire off an old extension cord or use almost any wire you have around.
Amazon has some for $4 with free shipping if you're odering other stuff at the same time. Any local hardware store carries them, too. Some clips have screws to attach the wires, and some have crimps you squash to hold the wire. You could get creative and wrap the wires around small chip clips or use bulldog clips or just wrap the wire around the battery post. The main thing is the wire needs to be in firm contact with the battery post.
I used a old 5-gallon bucket I had already. You can buy one at a hardware store for a few dollars. You can use any sort of bucket, even a plastic mop bucket or trash can. If you're desperate, a gallon milk jug might do.
This is just to tape up the splices in the wires. Stretch the tape and then wrap it around the splice. Afterwards it will try to shrink back to it's normal length and grip the splice tighter. That makes it more waterproof.
Obviously it would be better to solder the splices and use liquid electrical tape, but I wasn't that inspired. The leads are pre-tinned to make soldering easier.
There are waterproof splices you can order here.
The pump come with "Stainless Steel Shaft & Mounting Hardware".
Female garden hose connector
Nelson makes a female garden hose connector that fits either a 5/8" or 3/4" hose.
I used a short piece of 3/4" clear vinyl tubing. It fit right over the outlet discharge port/tube. If all you have is a 5/8" hose, you could split the end about 2", put it over the outlet and tape the heck out of it. Stretch the tape as you wrap and it will shrink back tightly afterwards. There is basically no pressure on the outlet hose so it's no big deal.