var builder = new ContainerBuilder();
builder.RegisterType<MyCustomConnection>()
        .As<ICustomConnection>()
        .PooledInstancePerLifetimeScope();
var container = builder.Build();
using (var scope = container.BeginLifetimeScope())
{
    // Creates a new instance of MyCustomConnection
    var instance = scope.Resolve<ICustomConnection>();
    instance.DoSomething();
}
// When the scope ends, the instance of MyCustomConnection
// is returned to the pool, rather than being disposed.
using (var scope2 = container.BeginLifetimeScope())
{
    // Does **not** create a new instance, but instead gets the 
    // previous instance from the pool.
    var instance = scope.Resolve<ICustomConnection>();
    instance.DoSomething();
}
// Instance gets returned back to the pool again at the 
// end of the lifetime scope.