If your bike has hydraulic disc brakes, they'll need bleeding every once in a while as part of your bike's regular maintenance. While this is something your local bike shop can help you with, you can save money by doing it yourself at home. Plus, it's a great skill to learn if you're interested in bike maintenance.
A brake bleeding kit gives you everything you need to remove old brake fluid and replace it with new fluid, to keep your hydro brakes operating as new.
Park Tool BKM-1 Hydraulic Bicycle Brake Bleed Kit - Mineral Oil
A universal mineral oil kit that will free up a hand
Park Tool does two universal brake bleed kits, and this is the one for mineral oil, which works best if your bike is running Shimano, Campagnolo, Magura, Tektro, Promax, TRP or Clarks brakes.
The kit includes two syringes, hoses with shutoff clips, multi-size bleed blocks, bleed funnel and a unique attachable syringe mount. The fittings are machined 7075 aluminum, and the entire kit comes housed in a rugged storage case to keep everything together and safe in your home workshop.
Replacement parts are also available, so while it's a bit of an investment, it will last you a very long time.
SRAM Standard Disc Brake Bleed Kit with DOT Fluid
A SRAM bleed kit for SRAM brakes
If you're running SRAM brakes then you'll need a kit that works with DOT fluid - luckily for you, SRAM already provides one.
This kit contains two bleed syringes with clamp tubes and fittings, two compression ferrules, barbed tubing inserts, four different bleed blocks, T10/25 Torx tool, T8 Torx tool, and more. It also comes complete with a 120ml bottle of DOT fluid so once you've got the kit you're good to go.
Brake Bleed Kit Bicycle Hydraulic Disc Brake Oil Mineral for Shimano, MAGURA, TEKTRO, SRAM Series Bike Brake Repair Tools
A cheap and cheerful bleed kit with lots of accessories
This is a pretty comprehensive bleed kit for the price, and includes a syringe, two piston blocks, a funnel, plug, bottle vent, tube, gloves, pothook and various other pieces necessary for a full bleed.
It also includes the tools you need: Torx screwdriver, 7-8 wrench, and adapters for M4, M5 and M6 screws. RSC Guide adapter and Universal adapters also included.
The fluid isn't included, but the kit is designed to be used with both mineral or DOT fluid, so is compatible with all disc brakes.