Using a marker float to explore your swim varies from water to water if you are on a gravel pit where there will be lots of underwater humps gulleys bars and plateaus clean areas and weedy areas you will have to spend a fair bit of time.The amount of marker float work you do will be dictated by the water you are fishing in.
Start of by casting to your left as far as you can then reel in and watch the rod tip and see how it feels if it feels like pulling through custard it tells you that the area is silt if the lead sticks then pulls out this tells you that you are in thick mud.
If the rod tip drags round that is weed you are into and it feels like the lead is jammed. If the rod tip knocks that is sand or gravel .If this area is surrounded by weed or silt this is a perfect area to put your carp bait in as you know the fish will be able to see your bait clearly.
To find out the depths of your swim using the marker float cast out again then wind down till the float jams up against the lead this will be shown by the fishing rod tip start to lock up.Then engage the baitrunner on your reel and start to pull of line one foot at a time.When the float breaks the water surface then you know what the depth is by the amount of line that you have pulled from your baitrunner reel.So drag the float in closer all the time feeling the bottom of the lake bed as you go.Bring it back about 10 to 15 yards or 10 to 13 metres whichever you prefer.Then repeat wind the float down, baitrunner on and measure line off your reel to find out the depth in the new spot.If the float does not pop up it is a sure sign that weed has clogged the line ring.Make some more exploratory casts and you might just find that fish holding feature you have been looking for to present your hookbait to.