Here in canada we can find it at Rona or Home Depot - any hardware store should have it. It is used for repairing leaks in plumbing, outdoor electrical
Good question! Depends on too many different variables: especially your body type. Muscle is negatively bouyant and body fat is positively bouyant. another important factor is if you are wearing a wetsuit, the thicker the wetsuit the more bouyant you will be and more weight will be needed. Also the amount of weight will change if you are doing dynamics in the pool vs open water where you'd would need significantly less weight
