What bottle brush do you use to clean a Waterpik SWI 615 Sinusense Water Pulsator?

There should be a plastic cap that can be removed to allow access to the pulsator retaining screw. When removed, the pulsator will lift out, The area and bottom of pulsator should be cleaned with a plastic bristled brush and hot white vinegar. A sanitation cycle should be run after reassembly.

Sounds like gum decease due to neglect of daily brushing, flossing, and finish with anti bacteria mouth wash. Myself, when I feel pain from tooth infection, I brush, floss, gargle with anti bacteria mouth wash, then irrigate with pressurized water using Waterpik. Seems to reverse tooth infection, but I never had gum decease, so I'm not sure this strategy would work on you, but I'm sure procuring Waterpik ($50) is cheaper than what dental hyginist would charge.

All detergents are basically sodium laurel sulphate or sodium loreth sulphate. Even toothpaste, hand soap, bar soap, laundry soap, dish soap contains this ingredient.
It allows oils to mix with water by reducing the surface tension so as to make the water molecules (packets) smaller. By doing so the molecules can get at and dissolve oils where it could not get to previously.
Water is already the worlds greatest universal solvent (every element on the periodic table has been found dissolved in water). Sodium laurel sulphate is toxic though and should never be in the human body and perhaps should never even touch the skin as it might be adsorbed.
It makes you wonder about toothpaste. No wonder they give instructions for children's use to not use more than the size of a pea. They suggest to rinse thoroughly. Detergents don't kill bacteria. They just help wash them away. Detergent washes any food that the bacteria may eat.
Keeping an item dry is the best way to kill bacteria. Antibacteria soaps will just help create a super bacteria or super virus. It will just make things worse over time.
Basically use any detergent... rinse well... keep it dry, and avoid the antibacteria soaps.

The Waterpik Ultra Cordless Dental Water Jet WP450 has pushbutton dual-pressure control system with low for sensitive gums (as well as high for deep cleaning).

I had the same problem for the longest time until today. I took a super soaker squirt gun (hand style with single pump on top) and shot it up the hole wear the water intake is for the pump (on the bottom of the white plastic part that has the trigger and water pump inside) while holding the trigger down to have the pump running, too. Did it a couple times for good measure. ;) When I tried it with the tank attached, it worked again. After that, I ran some rubbing alcohol through it to clean it up a bit but you could probably use hydrogen peroxide or distilled white vinegar as well. I'm guessing that the salt and baking soda mix eventually builds up and plugs it. Definitely plan on keeping the squirt gun handy in case it happens again. Hope this helps.

You just need to figure out which one you have and the manual should be on this site. If its not then give them a call.

http://www.waterpik.com/customer-service/instruction-manuals.html

You did not specify, I hope you are talking about the TRS-559 or TRS-553. Both come with a lifetime warranty, go to waterpik.com or call 1-800-525-2774