I picked up a new pump for this yesterday. It is a windshield washer pump from Princess Auto. No idea what it was in originally but it's in a Kenworth now.lol It had a relief valve with a really light spring. With no restriction it pumped like crazy(so did the original) but as soon as the pressure came up it dropped off. A quick dig through my spring container and I had a replacement that was sure to fix the issue. The new spring is so stiff that it has no relief

. Anyway, the unfortunate part is that the tank was made to fit around the old pump and of course the new pump although smaller, doesn't fit well. For now it is just crammed under the tank but I will have to carefully cut and modify the tank later.
She's pumps out 6l of water in just a few minutes now!
Videos are uploading of it in action.