There’s no sight quite as alarming as lifting the lid of your porcelain throne, only to find it’s betrayed you by not filling up with water. But fear not, DIY warriors! This friendly neighbourhood repairman is here to ease your plumbing woes and turn your toilet troubles into triumphant tales of bathroom brilliance.

Examining the Usual Suspects

In any detective story, there are always a few repeat offenders we need to keep an eye on. Same goes for our porcelain perpetrator. Let’s don our detective hats and sleuth our way through the common culprits of an under-filled toilet bowl.

1. The Infamous Fill Valve

The Fill Valve, also known in some circles as a ‘ballcock’, is the component that controls the amount of water that fills your toilet tank, and subsequently, your toilet bowl. One could say the Fill Valve is the 'Godfather' of toilet operations; therefore, its failure to provide might be causing your toilet bowl discrepancies.

Check the Fill Valve in the toilet tank. If it's set too low, the water level in your toilet bowl will be meager. Adjust the fill valve to a higher setting and see if that solves your problem. Turns out, sometimes the crime is just due to negligence!

2. The Troublesome Fill Tube

Otherwise known as the accomplice of the Fill Valve, the small, flexible tube plays an equally important role. The heist can still happen if the Fill Tube is dislodged or damaged.

If it's not attached to the overflow pipe or if it's cut too short, the water may not pour into the bowl correctly. Reattach or replace the fill tube to keep the partnership solid and the operation smooth.

3. The Dastardly Flapper

This rubber rascal seals the base of your tank and only lifts at your command (when you push the flush handle). The trouble starts when the flapper stays up for too long, causing most of the water to be directed into the sewer line instead of the bowl. Time to track down and tame your rogue flapper!

4. The Wily Water Valve

Hidden away, often behind the toilet, the water valve controls the flow of water to your toilet. If it has been accidentally or unexpectedly turned off, it could trick you into believing there is a more significant bathroom issue. Check the water valve and ensure it’s entirely switched on to quench the thirst of your dry toilet bowl.

Training For The Toilet Troubleshooting Tournament

Now that we unmasked our culprits, it’s time to train and polish your plumber’s prowess.

Ensure your supply line, pipes, and shutoff valves are functioning and without leaks. In this bathroom battle, you will be needing a few standard tools like a screwdriver and adjustable pliers. Fancy a deep dive into the world of DIY repair? Invest in a high-quality toilet repair kit. It’ll be your ultimate weapon, helping you address common toilet issues.

Calling For Back-Up

DIY-dive into your toilet bowl and wrestle with those components bravely. But remember, sometimes calling in a professional to help isn't a sign of defeat. It's your Batman signal, ensuring that your city (or toilet, in this case) will continue to thrive.

So, there you have it, folks! Our thrilling investigation into the not-so-mysterious case of the under-filled toilet bowl is concluded. If your toilet bowl not filling up with water was leaving you in deep waters, I hope these useful plumber-pro tips would've saved the day.

Learning how to fix minor issues not only saves you a chunk of change, it also teaches valuable skills and serves up a hearty dose of self-satisfaction. So, throw on your DIY cape and let the battle against the bathroom baddies continue! And remember, your local repairman is always here to lend a hand and a plunger if needed! Stay flush, my friends!