I just changed out my hot water heater yesterday and have low pressure (hot and cold) in one bathroom and an outside outlet. The bathroom had low pressure in comparison with the other bathroom for quite some time but now can hardly fill the pipes for a shower. The outside has never had any issues.

When I drained the old tank it had some slimy sludge in the bottom the consistency of melting jello but I didn't see any chips etc. I am on city water and pressure to the kitchen and other bathroom stayed the same. When I first filled the new tank I turned on the bathroom faucet that is having the problems and a lot of air came out and then some spitting of water/air. Same with the shower.

Would draining the tank again and refilling it have any effect or have I knocked some bad stuff loose? Oh, the bathroom and outside spigot are the closest plumbing to the hot water heater.

Thanks!

My bet's on crud being dislodged from the pipe walls when you replaced the water heater and now it's clogging up t6he bathroom and the hose bib. It won't help to drain the new heater it hasn't had time to build up any minerals, (more about that later).
You're going to have to turn off the water and open up the faucets and clear out any debris that's up there.
Now let's make sure it doesn't happen again.

For long life and fewer troubles you should keep your heater clear of mineral build-up by flushing on a regular schedule. Attach a hose to the boiler drain at the bottom of the tank. With the pressure on, open the boiler drain and let it run until the water runs clear. You will see a spurt of red,(rust) followed by white or yellow grains,(lime or calcium carbonate). This shouldn't take more then a few minutes. Do this monthly to keep it clear. Now flush out your hot water lines on ALL fixtures that are affected . Now pull each aerator and clean the screens. Be sure you put them back togather the same way you took them out. Don't forget to flush it out every month. Your heater will thank you for it. Hope this helps, Tom