Where in Pakistan can I buy a kettle BBQ

A couple of suggestions to help maintain constant heat.

1. Time it such that you are only adding a little fuel at any one time. Adding half new fuel will cool down considerably as it has to catch, burn, etc. Adding 10% fresh at one time is much better, for example.

2. Conversely, if you're lookin' you ain't cookin'. Open as little as possible. Remember there will be a lag to any specific change. If you change the vent, look at the temp after 5min then after 10min to see if the trend is up or down, and if it is accelerating or slowing. Use that as a guide to your next change.

3. Thermal mass is your friend. Get yourself some appropriate stones, bricks, etc. If you have any room left over from your fire and meat; fill the space with the bricks. They will help to smooth out the heat from open/closing as they take up space that would otherwise be taken by "cold" air when you open to refuel. Obviously you need to not block actual ventilation.

Overall the kettle is a nice grill; but leaves a little to be desired for smoking. The offset firebox style where you can refuel without disturbing the cook-box has a definite leg-up primarily for the refuelling reason; but with some practice you should still have wonderfully edible results with the kettle.

Happy Eating!

Piling the charcoal on one side gives you more control over your cooking -- because the grill isn't evenly hot, you can move the food around if its cooking too fast. In some cases, you specifically want the lower heat of indirect cooking, such as when dealing with roasts and other large cuts of meat.

The pan of water is often used when dealing with indirect cooking to reduce flare ups -- as the fat renders off, it lands in the water rather than the hot coals starting a grease fire and suddenly heating the item being grilled. As @deroberts points out, it also keeps the air moist, preventing the meat from drying out during the longer cooking period.

You always cover the grill to retain heat for indirect cooking; you're effectively creating an oven, so the item cooks evenly. Not covering the grill will mean your food won't cook evenly, if at al.

For thicker items (more than 2 inch / 5 cm thick), even if using direct cooking, you may wish to close the lid, rather than just cooking from the radiant heat of the coals. You will need to be careful, however, as it means you'll have to watch for smoke, as the fat renders off and falls into the coals. You should be prepared to open the lid to move the food should this happen, or keep a spray bottle of water to take down the flames.