if(belowTank2){
    if(tank_1.amount()>2*tank_2.amount()){
        valve.set_openRate(0.1);
        belowTank2=false;
    }
}else{
    if(tank_1.amount()<2*tank_2.amount()){
        valve.set_openRate(0.3);
        belowTank2=true;
    }
}